As the track density of an HDD increases in recent years, the problem of interference with an adjacent track is becoming serious. In particular, reducing side write due to the recording head magnetic field fringe effect is an important technical subject. A discrete track pattern medium (DTR medium) in which recording tracks are physically separated can reduce the side erase phenomenon that occurs during recording and the side read phenomenon by which information of an adjacent track mixes in during reproduction, thereby increasing the density in the cross track direction. This makes the DTR medium promising as a high-density magnetic recording medium. In addition, a bit patterned medium (BPM) physically divided in the bit direction as well has been proposed as a high-density magnetic recording medium capable of suppressing the medium noise and the thermal decay phenomenon by which recorded data disappears at room temperature.
Since the DTR medium and BPM are manufactured using the etching processing technique, the manufacturing cost may increase. Therefore, the following method has been proposed. That is, fine patterns obtained by EB (Electron Beam) lithography are transferred to a master, and an Ni stamper is duplicated from the master by electroforming. The Ni stamper is then set in an injection molding machine, and resin stampers are mass-produced by injection molding. The DTR media and BPM are manufactured by UV (UltraViolet-curing) imprinting using the resin stamper. This method can inexpensively mass-produce the DTR media and BPM. When patterns are downsized as the recording density increases, however, the ratio of the LER (Line Edge Roughness) to a master pattern increases in the manufacture of the pattern. Since the LER makes the recording density difficult to increase, demands have arisen for a method of suppressing the LER. On the DTR medium and BPM, not only information (a preamble, address, and burst) for positioning a read/write head but also recording tracks and recording bits are concentrically formed by EB lithography patterns that are transferred onto a master through an etching step. Since, however, an Si wafer conventionally used as the master is a single crystal and has etching anisotropy, the LER increases with respect to concentric patterns in portions different in crystallinity. To suppress the LER, an EB lithography resist can directly be used as the master. If an EB lithography resist pattern is directly used as the master, however, the resist pattern deforms due to the stress during electroforming. Therefore, a resist pattern cannot directly be used as the master when controlling a nanometer-order size. Also, a method of improving the linearity of a pattern by using an amorphous material as the pattern layer has been proposed. However, it is difficult to find an amorphous material by which fine patterns can be formed and to which conductivity can be given to such an extend that electroforming can be performed without any process gas damage.
To manufacture the DTR medium and BPM, it is common to transfer fine patterns whose size is 1/10 or less that of patterns formed on optical disks. When the patterns are downsized as the recording density increases, however, it has become difficult to duplicate the Ni stamper from the master by electroforming. Since a Si wafer used as the master is made of a single crystal and has etching anisotropy, highly rectangular patterns are obtained. Also, the hardness of the Si wafer is higher than that of the Ni electroformed film. When separating the Ni electroformed film (father stamper) from the master, therefore, the electroformed film is pulled by the Si master in a place where the rectangularity is high, thereby forming a burr. In addition, when a conductive film for performing electroforming is deposited by sputtering, the openings of fine patterns are closed to form cavities (pores) because the deposition rate of pattern projections is higher than that of pattern recesses. Since no electroformed film is formed in master recesses, pattern transfer defects occur. Furthermore, when performing duplication by electroforming, the conductive film peels off in a portion where the adhesion between the conductive film and electroformed film is weak, thereby producing a level difference corresponding to the thickness of the conductive film. Since the unevenness of the patterns of protrusions and recesses height of the stamper leads to pattern formation defects when manufacturing the DTR medium and BPM, the on-track BER (Bit Error Rate) increases.